Diamondback Moth (Lepidoptera: Plutellidae) in Cabbage: Influence of Initial Immigration Sites on Population Distribution, Density and Larval Parasitism

Abstract

Examinations of cabbage plants in five fields near Bunnell, Flagler Co., FL, in spring 1995 showed that larvae of the diamondback moth, Plutella xylostella (L.), were more abundant on the field ends (perpendicular to cabbage rows) adjacent to weed-filled drainage ditches than the fields ends abutting wooded swamp areas. There were no significant differences in the numbers of diamondback moth larvae on cabbage plants on the ends next to other cabbage fields or at sites located within the interior of the fields. Cabbage heads rated for damage due to diamondback moth larvae at harvest showed a distributional pattern similar to that observed for diamondback moth larvae. Parasitism of diamondback moth larvae was not significantly different between field ends and interior fields. Cabbage damage ratings on field sides (parallel to cabbage rows) showed that no edge effect was detected on the sides abutting other cabbage fields, that edge effect only occurred on the first one or few rows on the sides adjacent to other cabbage fields but separated by irrigation ditches, and that edge effect occurred continuously and decreased from the first to the 12th row on sides adjacent to earlier planted cabbage or an open weed-filled ditch area. These results suggest that diamondback moth first invaded cabbage fields from outside areas, and that more diamondback moth spread to the interior of the fields from adjacent open, weed-filled ditches than from bordering wooded and bushy areas.